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[85.165.210.26]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a2b1403f69sm668426e87.29.2026.03.28.14.35.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 28 Mar 2026 14:35:27 -0700 (PDT) From: Nikolaos Gkarlis To: netdev@vger.kernel.org Cc: kuba@kernel.org, nickgarlis@gmail.com, kuniyu@google.com Subject: [PATCH net v4] rtnetlink: add missing netlink_ns_capable() check for peer netns Date: Sat, 28 Mar 2026 22:33:38 +0100 Message-Id: <20260328213338.450601-1-nickgarlis@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit rtnl_newlink() lacks a CAP_NET_ADMIN capability check on the peer network namespace when creating paired devices (veth, vxcan, netkit). This allows an unprivileged user with a user namespace to create interfaces in arbitrary network namespaces, including init_net. Add a netlink_ns_capable() check for CAP_NET_ADMIN in the peer namespace before allowing device creation to proceed. Fixes: 81adee47dfb6 ("net: Support specifying the network namespace upon device creation.") Signed-off-by: Nikolaos Gkarlis --- v4: - Use IS_ERR_OR_NULL instead of IS_ERR + null check. v3: - Move netlink_ns_capable() check from rtnl_newlink() into rtnl_get_peer_net(), after the last rtnl_link_get_net_ifla(tb) call. The tbp path is already covered by rtnl_link_get_net_capable() in the caller. (suggested by Kuniyuki) - Pass skb to rtnl_get_peer_net() for the capability check. - Add IS_ERR() check on rtnl_link_get_net_ifla(tb) return value. v2: - Removed "Reported-by" tag - Fixed "Fixes" tag with the help of Kuniyuki Iwashima (thanks !) net/core/rtnetlink.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c index fae8034efbf..a4d8fd8232e 100644 --- a/net/core/rtnetlink.c +++ b/net/core/rtnetlink.c @@ -3894,12 +3894,14 @@ static int rtnl_newlink_create(struct sk_buff *skb, struct ifinfomsg *ifm, goto out; } -static struct net *rtnl_get_peer_net(const struct rtnl_link_ops *ops, +static struct net *rtnl_get_peer_net(struct sk_buff *skb, + const struct rtnl_link_ops *ops, struct nlattr *tbp[], struct nlattr *data[], struct netlink_ext_ack *extack) { struct nlattr *tb[IFLA_MAX + 1]; + struct net *net; int err; if (!data || !data[ops->peer_type]) @@ -3915,7 +3917,16 @@ static struct net *rtnl_get_peer_net(const struct rtnl_link_ops *ops, return ERR_PTR(err); } - return rtnl_link_get_net_ifla(tb); + net = rtnl_link_get_net_ifla(tb); + if (IS_ERR_OR_NULL(net)) + return net; + + if (!netlink_ns_capable(skb, net->user_ns, CAP_NET_ADMIN)) { + put_net(net); + return ERR_PTR(-EPERM); + } + + return net; } static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, @@ -4054,7 +4065,7 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, } if (ops->peer_type) { - peer_net = rtnl_get_peer_net(ops, tb, data, extack); + peer_net = rtnl_get_peer_net(skb, ops, tb, data, extack); if (IS_ERR(peer_net)) { ret = PTR_ERR(peer_net); goto put_ops; -- 2.34.1